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International Nuclear Event Scale

The International Nuclear Event Scale is used to define the seriousness of nuclear accidents. This scale, named INES for International Nuclear Event Scale, is a public relations tool intended for the media and the general public. It is not a crisis management tool, nor is it for comparison between countries.

The principle of the international nuclear event scale

The international nuclear event scale has 8 degrees of seriousness from 0, a simple anomaly, to 7 for a very severe accident of the Chernobyl type. In fact it was following this disaster that the International Atomic Energy Authority (IAEA) created INES to make it easier for the general public to understand the scope of nuclearincidents and accidents.

Events of seriousness 0 are not always reported. From 1 to 3 events are qualified as incidents, beyond this, as accidents.

The degrees of seriousness

The determination of the degree of seriousness depends on three factors:

  • the impact on in-depth-defence (safety measures to delay the appearance of an impact);
  • the impact on the site;
  • the impact off the site.

The most frequent events are of degree 0 or 1. Only the Chernobyl and Fukushima disasters have been classified 7.

Application of the international nuclear event scale

Around sixty countries have adopted this scale, but there is no harmonisation in event classification among these countries.

The scale of seriousness of nuclear events. © AIEA The scale of seriousness of nuclear events. © AIEA



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